Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

129
FXUS63 KLOT 101736
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1236 PM CDT Wed Jun 10 2026

.KEY MESSAGES...

- Today and Thursday will be hot and humid with multiple rounds
  of severe storms.

- Thursday continues to look like the day of greatest concern
  for severe weather with a threat for all hazards (tornadoes,
  damaging hail, damaging winds, and flash flooding)

- Friday and Saturday will be dry and noticeably cooler. A
  generally cool and at times wet pattern will develop next
  week.

&&

.UPDATE...
Issued at 931 AM CDT Wed Jun 10 2026

Morning water vapor imagery reveals weak, broad rotation about
a shortwave perturbation pushing into western MO/southwestern IA
and moving northeast as it traverses the leeward side of the
larger upstream trough. With the help of a low level jet
impinging on the wave from the west (KEAX VWP sampling 50 kt
down to ~500 ft AGL), elevated convection began going up near
and west of Kansas City just after sunrise and coverage
continues to expand in this vicinity, now advancing into
southwest IA and north-central MO as of this writing around 9
AM. This cluster will be the one to watch for our first
potential round of severe weather beginning early-mid afternoon.

12Z RAOB out of ILX depicts a warm nose at the base of an EML
defined by 7.5-8 K/km lapse rates extending from 850mb up
through the mid levels. The balloon sampled nearly 3,500 J/kg of
elevated instability while 0-6 km shear came in at a meager 13
kt. Between efficient diurnal heating as well as some dynamic
cooling in the 800-700 mb layer, the cap is expected to erode
nicely by the time storms reach our area in the afternoon. 13Z
SPC mesoanalysis suggests CIN is already dwindling quickly over
northern IL. Latest CAM guidance resolves 3,000 to 3,500 Joules
of uncapped surface-based CAPE building into the afternoon.

The camps that have been better handling current conditions
upstream have the storms arriving in our west between 2 and 3 PM
and working across our area into the early evening. However,
those storms do appear to be moving faster than modeled at 40 to
45 mph toward the northeast, which would get them here a bit
earlier in the afternoon if that continues. Storms should become
surface-based before long, and guidance favors storm mode
evolving from clustered supercells into a bowing MCS on their
way across northern and central IL. Damaging to locally
destructive wind gusts remain our biggest concern with storms
this afternoon; a number of CAMs explicitly resolve pockets of
60 to 70+ mph gusts in our area. Small to marginally severe hail
is certainly on the table given the instability, but the weak
shear and high freezing levels are generally unfavorable for
damaging hail. The tornado threat is also on the lower side, but
non-zero. There`s a very good chance that storms will be cold
pool dominant as they move across. However, if storms can remain
surface-based, some low level veering and lots of low level
instability could conceptually result in a quick spin up or two,
but poor effective shear for overall storm organization and
surface winds more veered than previously modeled greatly
dampens an appreciable tornado threat. The likelihood of
tornadoes and severe hail decreases with eastward extent across
northern IL.

In general, very little has changed in expectations since the
morning forecast package. Updated forecast products will be sent
shortly. For details regarding this evening storms chances and
expectations for Thursday, see the full discussion from this
morning below.

Doom

&&

.DISCUSSION...
Issued at 242 AM CDT Wed Jun 10 2026

Today and Tonight:

Early morning GOES-19 water vapor imagery depicts aggregate
upper-level troughing centered over the northern Rocky Mountain
region. There are several upper-level shortwaves embedded
within the expansive cyclonic flow, including one currently
supporting a squall line moving across western Minnesota and
another in the central Plains. Meanwhile, an elevated warm
frontal zone is lifting northeastward across southern Wisconsin,
northern Illinois, and northeastern Indiana this morning as
identified by a zone of persistent ACCAS visible on GOES-19
nighttime microphysics imagery RGB imagery. So far, there have
only been a few attempts for convection to initiate within the
warm frontal zone this morning. At this point, am cautiously
optimistic we are out of the woods for an isolated severe storm
(call it a remaining 10% chance). Finally, a region of marine
fog is stalled across portions of Lake and far northeastern Cook
county this morning. The lowest visibility (one quarter of a
mile) remains confined roughly near and east of I-94, and will
continue to handle the locally reduced visibility with a Special
Weather Statement through 5:30 this morning.

The stage is set for a hot and stormy day. After daybreak, the
elevated warm frontal zone will shift northeast of our area.
Warm overnight lows (current temperatures are largely in the low
to mid 70s) will act as a springboard for temperatures to race
into the mid to upper 80s by late morning. When combined with
dew points in the low to mid 70s, heat index values are expected
to reach 95 to 100 degrees by noon. Focus then turns to the
potential two windows for severe weather today.

The first window will be in the afternoon (1 to 6 PM) as the
aforementioned upper-level shortwave currently in the central
Plains races into the Lower Great Lakes. Ahead of the wave, the
overlap of steep mid-level lapse rates (sampled near 8 K/km per
the 00Z DVN RAOB), moist low-to mid-levels (mean 1km mixing
ratios of nearly 17 g/kg and PWATs near 2 inches sampled by the
same 00Z DVN RAOB), and warming boundary layer temperatures into
the upper 80s will lead to the development of appreciable
instability characterized by MLCAPE >3000 J/kg. While deep-layer
shear will be lower than typical for severe weather days with
the first wave (effective and cloud-layer shear in the
neighborhood of 30-35kt), the strong instability and deep
moisture profiles will quickly encourage initial cellular
development in eastern Iowa to merge into one or more outflow-
dominant clusters with a threat for damaging to locally
destructive winds (60 to 80 mph). The highest coverage is
favored to be along and north of I-80 tied to the core of the
wave, though at least scattered coverage may occur as far south
as the US-24 corridor.

The second window for severe storms today will be in the
evening hours (6 to 10 PM) as a secondary upper-level shortwave
races into the Midwest. While the core of the upper-level wave
will track decidedly northwest of our area, increasing
isentropic ascent atop what would probably be an outflow-
reinforced warm front draped across eastern Iowa and northern
Illinois would nevertheless support renewed thunderstorm
development. Now, the intensity of renewed development including
any potential for severe weather is unclear, as the highest
coverage of storms may end up north of the outflow-reinforced
warm front. With that said, any storms that develop near and
south of the front would be capable of producing damaging winds.
Suppose there could be a conditional threat for QLCS tornadoes
should any bowing segment develop and intersect the outflow-
reinforced warm front, as well. Coverage of storms should
decrease from northwest to southeast during the evening hours.

At this point, the expectation is for combined cold
pool/outflow pushes from the two rounds of storms to temporarily
push the warm front south of our area by midnight. Assuming
this occurs, any threat for festering convection driven by the
low-level jet riding atop the frontal boundary should be south
of our area across central Illinois giving our local area a
break.


Thursday:

Thursday continues to look like a day of greater concern for
severe weather. Ensemble model guidance remains steadfast that
the most dominant shortwave embedded in the aggregate cyclonic
flow in the northern US will pivot northeastward into the Great
Lakes on Thursday. Surface pressure falls west of the
Mississippi River ahead of the wave will consolidate into a
coherent surface low in central Iowa, leading to rapidly
increasing low-level southwesterly flow across the middle
Mississippi River Valley. As a result, the expectation is for
the warm front to rapidly retreat northward into eastern Iowa,
northern Illinois, and possibly southern Wisconsin by midday
Thursday. (Accordingly, Thursday will be another hot and humid
day for much of our area with peak heat index values in the
upper 90s to around 100).

Like today, there may be two rounds of severe weather tomorrow.
Curiously, CAM guidance continues to depict the development of
thunderstorms across Nebraska and Iowa late tonight potentially
tied to mid-level gravity waves emanating from unbalanced
upper-level flow. (The HRRR in particular does depict GWAC
supercells in central Iowa by daybreak). At this point, current
thinking is morning activity would be poised to lift
northeastward toward northeastern Iowa, northwestern Illinois,
and southern Wisconsin (more specifically, northwest of a line
from Dixon to Crystal Lake) in the 11 am to 2 PM timeframe.
Even while any early-day convection would probably remain north
of the warm front, strengthening upper-level shear ahead of the
approaching short wave and steep mid-level lapse rates would
still support a threat for damaging hail up to 2 inches in
diameter. If the storms do end up tied to gravity waves, would
have to watch for corridors of destructive winds (70+ mph) as
well. Will note that sometimes these morning rounds of storms in
these kinds of patterns can end up somewhat unexpectedly
impactful given so much attention on the afternoon period.
Speaking of which...

The second window for severe weather will be during the
afternoon and evening hours (3 to 9 PM) as the upper-level
shortwave ejects into the Great Lakes. An ensemble of CAM
guidance is in agreement that the associated surface low will
deepen toward the lower 990s mb range while lifting
northeastward into central Wisconsin Thursday afternoon.
Thunderstorm development is favored both along the northward-
moving warm front and along the eastward-moving cold front by
late afternoon.

With MLCAPE >2500 J/kg and effective shear >50kt, the
environment within the warm sector of the cyclone will be very
supportive of severe weather. At this point, the expectation is
for initial supercell development along both frontal zones with
a threat for all hazards (tornadoes, damaging winds, damaging
hail) with eventual upscale growth into a southeastward-racing
squall line. Of particular concern is the rapid increase in low-
level flow on the southeastern flank of the surface low during
the evening hours, which will lead to 30 to 40 kt of 0-1km shear
and over 300 J/kg of SRH for eastward-moving storms especially
along the warm front in northern Illinois or southern Wisconsin.
Accordingly, should supercell storm modes be maintained along
the warm front, there will be a threat for strong (EF-2+)
tornadoes. Thunderstorm coverage is expected to end from
northwest to southeast across the area as the evening
progresses.

Not to be forgotten, the potential for up to four rounds of
severe thunderstorms within a high-PWAT airmass in the next 48
hours raises concern for flash flooding. The rounds of
thunderstorms today will likely "prime the pump" for a more
noteworthy flash flood threat tomorrow, especially considering
storms today should be more progressive and storms tomorrow may
have a better opportunity to train along the warm frontal zone.
Indeed, the 00Z 48-hr PMM QPF depicts a wide swath of 3 to
locally 7 inches of rain centered on eastern Iowa, southern
Wisconsin, and northern Illinois. Meanwhile, combined 24-hour
LPMM QPF from the experimental REFS (no 48-hour PMM available)
depicts potential for pockets of up to 8 inches of rainfall
through Thursday evening. Did consider hoisting a Flood Watch
this morning, but felt it would make more sense to do so either
on the day shift today or midnight shift tonight (again focusing
on the more pronounced threat on Thursday). Also, did touch
base with WPC on the potential need for an upgrade to the
current Level 2/4 threat level for flash flooding valid for
Thursday.


Friday onward:

A break in the hot and stormy pattern is expected Friday and
Saturday as a surface high pressure system works through the
region. Highs on Friday should top off in the upper 70s (locally
80), and lows Friday night should fall into the lower 60s.
Ensemble guidance than depicts the development of expansive
troughing across the northern United States next week. While the
main reservoir of hot and humid air would get shunted well
south of our area, a parade of shortwaves may lead to periodic
opportunities for showers and thunderstorms across our region
through next week.

Borchardt

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1236 PM CDT Wed Jun 10 2026

Key Aviation Messages for the current TAF period:

- Three rounds of strong to severe storms is expected to impact
  regional terminals through the TAF window.

A very active period of weather impacting regional terminals
over the course of the next 36 hours. Currently, conditions are
VFR with southwest wind gusts 20 to 25 knots. However,...

Round 1 (this afternoon):
A complex of showers and storms currently (at the time this
discussion was published) over eastern Iowa is expected to move
over northern Illinois, sending a line of strong to severe
storms across the state impacting regional terminals. The
primary concern during this window is for strong and damaging
winds and downpours that reduce vis down to IFR conditions.
Adjusted the TEMPO to account for the earlier than expected
arrival time and narrow down the window for the line to pass
over TAF sites.

Round 2 (this evening through midnight):
There is lower confidence in whether or not VFR showers may
linger between Rounds 1 and 2, but the thinking is that there
could be a break in the weather for a bit. But after 00Z, a
surface boundary will pass over northern Illinois for an
additional line of showers and thunderstorms at area terminals.
While the severe risk is lower than Round 1, it remains non-
zero, with the main hazards still being damaging winds and heavy
rain. With models coming into better agreement with this
window, the PROB30 was converted to a TEMPO with timing adjusted
to a slightly later arrival. Lastly, the VRB wind direction was
kept in the TEMPO to account for a brief pressure drop behind
the line which may cause winds to become squirrelly for a time.

While timing for Round 2 may be adjusted in later TAF packages,
there is higher confidence in VFR and drier conditions
developing once this line exits to the east-southeast through
the rest of the morning and early afternoon.

Round 3 (late tomorrow afternoon):
A cold front is expected to move across northern Illinois
tomorrow bringing another round of strong to severe storms over
the region. All severe hazards (damaging winds, hail, flash
flooding, and tornadoes) is on the table with storms tomorrow.
The primary window for this event may be after 00Z, but
confidence in its arrival as early as 23Z was high enough for
mention in the Chicago terminal TAFs.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 9 PM CDT this evening for the IL
     and IN nearshore waters.

&&

$$

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